1. Field of the Invention
The present invention relates to a plasma processing process and apparatus useful in the fabrication of integrated circuits (ICS) or similar semiconductor devices, More particularly, the present invention relates to a microwave plasma processing method and process and an apparatus used for an etching or ashing process in the fabrication of ICS or similar devices. The present invention enables processing of a material at a higher speed by significantly reducing the reflection of microwaves.
2. Description of the Related Art
In a process for forming fine patterns in ICS or similar semiconductor devices, an etching or ashing process based on a dry process is widely used. A typical dry etching process is the plasma etching process. The plasma etching process, as compared with the wet etching process, which was frequently used at the beginning of the IC industry, has various advantages such as fine resolution and less undercutting, reduction of the number of fabricating processes by elimination of wafer handling for rinsing and drying, etc., and inherent cleanliness: Plasma etching, in particular, makes it possible to perform sequential etching and stripping operations on the same machine, making it possible to have a fully automated fabricating process for ICS or similar devices.
A "plasma" is a highly ionized gas with a nearly equal number of positive and negative charged particles plus free radicals. The free radicals are electrically neutral atoms or molecules that can actively form chemical bonds. The free radicals generated in a plasma, acting as a reactive species, chemically combine with materials to be etched to form volatile compounds which are removed from the system by an evacuating device.
Recent conventionally used plasma etching apparatuses comprise a plasma generating region (plasma generating vessel or generator) and a reacting region (reactor or etching chamber) spaced apart from each other and connected through a tube or waveguide to guide the microwaves from the plasma generating vessel to the reactor. In these apparatuses, the reactor has a microwave transmission window of silica or ceramic disposed perpendicular to the flow direction of the microwaves in the waveguide. The microwave plasma etching apparatus of the above-described structure is hereinafter referred to as a "perpendicular incidence-type plasma etching apparatus".
Examples of the perpendicular incidence-type microwave plasma etching apparatus can be found in patent literature, such as Japanese Examined Patent Publication (Kokoku) Nos. 53-14472, 53-24779, and 53-34461; Japanese Unexamined Patent Publication (Kokai) No. 53-110378, and U.S. Pat. No. 4,192,706, which is a counterpart of Japanese Examined Patent Publication (Kokoku) No. 53-14472.
In the conventional apparatuses, however, the processing rate is low as a result of the reflection of the microwaves at the two interfaces of the microwave transmission window. Further, matching of the microwaves is difficult because the microwaves are not effectively transmitted into the reactor. Furthermore, it is not easy to cool the stage for the object under processing or to reduce the size of the apparatus.